A type of water jug that is widely used has a substantially cylindrical side wall, a substantially flat bottom wall, and a valved outlet tap or faucet through the side wall, at a level just above the bottom wall, through which the contents of the jug can be drawn off as required. Such jugs are frequently used by travelers, who must fill the jug from whatever water supply is available. Since the jug often provides the only source of drinking water that is readily accessible, the purity of the water dispensed from it is a matter of great importance. If the source from which the jug is filled is suspected of being contaminated with disease germs, a germicidal preparation can be added to the water, but this does not solve the problem of removing sand, silt, rust, scale and other filterable foreign matter that may be present in it to impair its palatability.
It is obvious, therefore, that the provision of a suitable filter in a water jug of the character described would be useful and desirable. In fact, it has been found that there is a strong demand for such a filter in certain areas where pure, clean drinking water is relatively scarce.
A filter unit satisfactory for installation in a jug of the character described must meet several requirements.
The filter must obviously be effective, and this means that it should incorporate activated charcoal pellets or granules for removal of gases that impart taste and odor to water. However, a water jug is often subjected to shaking and jostling that tends to break up charcoal, and therefore the charcoal should be enclosed in filter paper or the like that will prevent small particles of it from passing out with the dispensed water.
The filter paper picks up sand, silt and the like that may be present in the water, but it is rather fragile and must be adequately protected from being punctured by ice cubes dropped into the jug.
The filter must be so arranged that all water flowing to the tap or faucet at the bottom of the jug is constrained to pass through it. Hence there must be a seal between the filter and some part of the jug, whereby unfiltered water is prevented from flowing to the tap inlet. To further complicate the problem, the jug normally has a smooth interior surface, but the inside diameter of its cylindrical side wall is not necessarily maintained within close tolerances, so that a sealing connection of a filter to the jug side wall is impractical. Of course the connection between the jug and the filter must be a secure and sturdy one, capable of supporting the jostling, bumping and tilting to which the jug may be subjected; but the filter must nevertheless be readily removable from the jug for cleaning or replacement.
From a functional standpoint, the filter should be able to remove all filterable solids from the water, and therefore it must necessarily present substantial resistance to flow of water through it. In view of this, the filter should have a relatively large effective surface area, so that even though flow of water through any one small unit of its surface area is relatively slow, the total flow of filtered water through is at a satisfactorily fast rate. With a large surface area, there is also the advantage that a large volume of turbid water can be put through the filter before it needs cleaning or replacement.
A further important requirement is that the filter be as compact as possible, because the water volume capacity of the jug is necessarily reduced by the volume of the filter. Furthermore, the filter should be so arranged that it traps no more than a negligible quantity of water in a part of the jug where it cannot pass through the filter and into the outlet tap.
While meeting all of these requirements, the filter unit must nevertheless be as inexpensive as possible.
Heretofore no filter unit has been available that meets the several objectives set forth above. Perhaps the nearest approach to a device that might serve the purpose is disclosed by U.S. Pat. No. 4,181,243, to Frahm, which discloses a filter cartridge for a water cooler of the type having an open-top reservoir on which a large water bottle is supported in inverted position. A tap or faucet at the bottom of the reservoir has a screw-threaded tubular inlet stem which extends through the side wall of the reservoir and is secured by a nut at the inside of that wall. A cup-shaped holder into which a filter cartridge is push-fitted has a coaxial threaded hole in its end wall whereby it is screwed onto the inwardly projecting end portion of the faucet stem. The filter cartridge is relatively small, and it would have to be even smaller if it were adapted to a water jug, wherein the outlet tap is located as near as possible to the bottom wall, since the radius of the cup-shaped holder would have to be a little smaller than the small distance from the center of the tubular faucet stem to the bottom wall. Even in the water cooler installation in which it is shown, the filter cartridge of the Frahm patent necessarily has a relatively small surface area; in a water jug installation it would have an unsatisfactorily small filtering capacity and would choke the outflow of water to a slow trickle.
U.S. Pat. No. 2,477,998 to McCowan discloses a dispenser wherein bar soap is dissolved in water to be dispensed as a liquid. The soap rests on a screen which could be regarded as a type of filter and which extends across the entire interior of the container, a little above its bottom, supported on the top of a wide funnel that leads down to a valved outlet duct in the bottom of the container. In the disclosed device it is of no consequence that a certain amount of water can bypass the screen by flowing around its edge, but a true filter arranged in the same manner as that screen would have to be sealed to the side wall of the container. In this and other obvious respects the arrangement suggested by McCowan would be unsatisfactory for a filter for an existing water jug of the character described.
U.S. Pat. No. 3,392,837 to Sanzenbacher discloses a water container of rather complicated configuration that has its outlet specially formed to accommodate a filter cartridge. The disclosed arrangement is obviously unsuitable for existing water jugs, and especially those of the thermally insulated type.